Ammonia for post-healing of formamidinium-based Perovskite films

Solvents employed for perovskite film fabrication not only play important roles in dissolving the precursors but also participate in crystallization process. High boiling point aprotic solvents with O-donor ligands have been extensively studied, but the formation of a highly uniform halide perovskite film still requires the participation of additives or an additional step to accelerate the nucleation rate. The volatile aliphatic methylamine with both coordinating ligands and hydrogen protons as solvent or post-healing gas facilitates the process of methylamine-based perovskite films with high crystallinity, few defects, and easy large-scale fabrication as well. However, the attempt in formamidinium-containing perovskites is challenged heretofore. Here, we reveal that the degradation of formamidinium-containing perovskites in aliphatic amines environment results from the transimination reaction of formamidinium cation and aliphatic amines along with the formation of ammonia. Based on this mechanism, ammonia is selected as a post-healing gas for a highly uniform, compact formamidinium-based perovskite films. In particular, low temperature is proved to be crucial to enable formamidinium-based perovskite materials to absorb enough ammonia molecules and form a liquid intermediate state which is the key to eliminating voids in raw films. As a result, the champion perovskite solar cell based on ammonia post-healing achieves a power conversion efficiency of 23.21% with excellent reproducibility. Especially the module power conversion efficiency with 14 cm2 active area is over 20%. This ammonia post-healing treatment potentially makes it easier to upscale fabrication of highly efficient formamidinium-based devices.

common apex angle connecting. The A site ions fill up the gap of the octahedral and the structure is stabilized by Van der Waals forces 3 . These special structural characteristics provide a variety of solution processing methods to prepare perovskite films [4][5][6] .
The high boiling point aprotic N,N-dimethylformamide (DMF), γbutyrolactone (GBL), dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMA) are the common solvents employed to dissolve the perovskite precursors with the formation of solvated iodoplumbate complexes because of the strong coordination between O-donor ligands (OLs) and Pb(II) 4,[7][8][9] . The Lewis basicity of solvents is thought to correlate with the "coordinating ability" with lead halide salts, which can be predicted by their Gutmann's Donor Number (D N ) with a trend of DMSO > DMA > DMF > GBL 10,11 . High D N solvents with strong coordination with the Pb(II) center also result in the formation of intermediate phase OL-PbI 2 -RAI (RA refers to MA or FA, etc.) prior to perovskite phase during the film fabrication process. The anisotropic growth nature of the intermediate phase leads to rough films with onedimensional (1D) fiber-like structures and a large proportion of void area 12 . In this regard, stronger coordinating additives (such as thiourea 13 and pyridine 14 ) and/or the fast nucleation strategies (such as anti-solvent extraction, gas-quenching, and vacuum-assisted drying) have been introduced to regulate the growth process of the intermediate phase to achieve highly uniform perovskite films with good crystallinity 7,15,16 .
Among them, methylamine (MA 0 ) featured with the presence of hydrogen bonding and low boiling point has become an impressive coordination agent for the MAPbI 3 material. In this case, the formed intermediate phase is a metastable (PbI 2 -MAI)·xMA 0 complex, instead of simple coordinate bond-dominated OL-PbI 2 -MAI adducts. Easy formation of highly uniform (PbI 2 -MAI)·xMA 0 films and following conversion to highly uniform perovskite films are closely related to the self-leveling behavior of (PbI 2 -MAI)·xMA 0 liquid intermediate phase and the ultrafast evaporation of MA 0 gas. MA 0 employed as a posthealing gas to eliminate the voids in the MAPbI 3 perovskite film is firstly reported by Zhou et al. in 2015 17 , and the adoption of MA 0 as a volatile solvent system has become a commercially viable technology for MAPbI 3 devices with excellent device reproducibility [18][19][20][21][22][23] . In comparison with MAPbI 3 , α-FAPbI 3 has higher theoretical efficiency and thermal stability. The undesired phase transition to non-perovskite phase δ-FAPbI 3 has been well dissolved by alloying a small amount of Cs + , MA + to tailor the tolerance factor [24][25][26][27][28][29] . We have attempted to introduce MA 0 gas-related methods for the fabrication of FAcontaining perovskite layers, unfortunately, resulting in degradation of the 3D perovskite phase 18 . The underlying reason for the irreversible transformation of FAPbI 3 with MA 0 treatment is still not fully clear, let alone make efforts to solve this problem.
Here, we have systematically studied the underlying chemical reactions between aliphatic amines/formamidine (FA 0 ) gases and FAI salt, and elucidated the addition-elimination reaction between amine compound and the imine band of FA 0 with the formation of ammonia (NH 3 ), also named transimination reaction. Based on this mechanism, NH 3 is selected as a post-healing gas to avoid the degradation of the FA-based perovskite phase during the post treatment. It is demonstrated that decreasing processing temperature is crucial for FAbased perovskite layer to enhance the absorption of NH 3 molecules, leading to the formation of a desired liquid intermediate state. Selfleveling behavior of the liquid intermediate state can quickly heal the voids in the rough perovskite film and finally form a highly uniform and compact film with the evaporation of NH 3 . At last, the PCE of FAbased PSC based on this NH 3 post-healing strategy is more than 23% with a certified PCE of 22.22%. Especially, the PSC module achieves a PCE of 20.61% which is comparable with the highest reports in PSC modules. These results demonstrate the large advantage of the NH 3 gas post-healing technology in upscaling fabrication of highly efficient PSCs.

Results
The degradation evidence of formamidinium-containing perovskites in aliphatic amines environment Nuclear magnetic resonance (NMR) spectroscopy is a particularly practical tool for quantifying the relative amounts of the organic cations and related chemical reactions in the perovskite precursor [30][31][32][33] . We started with the study of the underlying chemical reactions between FA 0 /R-NH 2 (RA 0 ) gases and FAI salt ( Table 1). The gases involved include FA 0 , MA 0 , ethylamine (EA 0 ), n-propylamine (PA 0 ), nbutylamine (BA 0 ), and NH 3 . The detailed preparation procedures of the relevant gases are provided in the methods section.
The synthesis of FA 0 is tricky because of its instability. Mixed FACl and NaOH powders are expected to form FA 0 by the neutralization as shown in Supplementary Scheme 1a. To study their product, deuterated DMSO (DMSO-d 6 ) solvent is used to collect released gas from the mixed powders at room temperature (RT) by a simple equipment (Supplementary Fig. 1a Supplementary Fig. 4). We think that the high boiling point of FA 0 likely makes FA 0 molecules difficult to diffuse into DMSO-d 6 solvent. The formation of NH 3 is indicative of the existence of some chemical reactions in the process of gas preparation ( Supplementary Fig. 2). When the temperature of the reactor and the gas pipeline is increased to 150°C and DMSO-d 6 solvent is still kept at RT, four main compounds are detected: s-triazine, formamide, FA 0 , and NH 3 (Table 1 (No. 2) and Supplementary Fig. 5). The formation of s-triazine is because of the transimination reaction of three FA 0 molecules along with the formation of NH 3 ( Supplementary Fig. 2b) 30,31 . The s-triazine has also been detected when the FAI powder is heated at 150°C 32 . Formamide is attributed to the hydrolyzation product of FA 0 ( Supplementary Fig. 2c) in the presence of H 2 O which is generated from the neutralization between FACl and NaOH. Considering the long-time interval from gas collection to 1 H NMR measurement, we then employ acetic acid (HOAc) to capture FA 0 so as to limit these chemical reactions in DMSOd 6 solvent by the quick formation of FAAc. As expected, 1 H NMR spectrum verifies that the reaction product at 150°C only exists FAAc rather than s-triazine, formamide, or NH 4 Ac ( Table 1 (No. 3) and Supplementary Fig. 6). The above results strongly indicate the formation and instability of FA 0 . When FAI powder is exposed to FA 0 , there is hardly any change in chemical compositions except the formation of a tiny amount of formamide as the presence of H 2 O (Table 1 (No. 4), Supplementary Fig. 7). These spontaneous reactions and instability of FA 0 seriously limit its practical application in post-healing FA-based perovskite films.
In comparison with FA 0 , amines are more stable. When FAI powder is treated with MA 0 , EA 0 , PA 0 , or BA 0 , the powder quickly transforms into a liquid state. After the liquid is held at 60°C for 6 h and then vacuumed ( Supplementary Fig. 1b), it is unexpected that there are no FAI signals in 1 H NMR spectrum of the final powder samples (  33 . The related chemical reactions are illustrated in Fig. 1 (i, ii). The lone-pair electrons of N atom in nucleophilic MA 0 molecule can attack electrophilic imine bond in FAI, which leads to the formation of N-methyl formamidinium iodide (MFAI) by a transimination process ( Fig. 1(i), Supplementary Fig. 3) 34 . The imine bond in the formed MFAI can carry out the second transimination reaction with MA 0 to form DMFAI ( Fig. 1(ii), Supplementary  Fig. 3). With excessive MA 0 and holding for enough time, FAI can fully transform into DMFAI. Similarly, when FAI powders are treated with EA 0 , PA 0 and BA 0 gases, the transimination reaction also occur with the formation of DEFAI, DPFAI and DBFAI, respectively (  Fig. 1 When FAI powder is treated by RA 0 (R is referred to H, Me, Et etc.) gas with some H 2 O vapor evaporated from their aqueous solution ( Supplementary Fig. 1c), the final product is RAI rather than FAI, RFAI or DRFAI (  Fig. 15), the formation of RAI mentioned above is due to the reversible ion exchange reactions between FAI, RFAI or DRFAI and RA 0 with the formation of RAI and FA 0 , RFA 0 , or DRFA 0 . The hydrolysis reactions of FA 0 , RFA 0 , and DRFA 0 lead to the formation of volatile HCOOH and RA 0 , which in turn promotes the ion exchange reactions towards the formation of RAI ( Fig. 1 (iii-x)) 35 . Supplementary Fig. 16 shows the optical photos and XRD patterns of α-FAPbI 3 films before and after MA 0 post-healing treatment. δ-FAPbI 3 , MFAPbI 3 , and DMFAPbI 3 films are also measured for comparison. The formation of the non-perovskite phase after MA 0 post-healing the α-FAPbI 3 film is because of the conversion from FA + to MFA + and DMFA + . This is why aliphatic amines cannot be employed as solvents or post-healing gases for the fabrication of FA-containing perovskite materials. Inspired by the above transimination reaction, NH 3 is selected to avoid the change of composition after the gas post-healing treatment. The 1 H NMR spectrum well verifies no composition change of FAI powder after being treated with NH 3 gas (Table 1 (No. 13), Supplementary Fig. 17).

Feasibility analysis of ammonia as the healing gas
The reversible absorption-desorption process of gas is crucial for the post-healing strategy. MAI and FAI samples are weighted during MA 0 / NH 3 absorption and desorption as shown in Fig. 2a. The whole process can be divided into gas absorption at RT (Stage I), desorption at RT (Stage II), and desorption at 80°C (Stage III). When exposed to MA 0 , MAI quickly absorbs MA 0 and reaches a saturated state with the x value of about 2.5 in MAI·xMA 0 (the x value is very sensitive to temperature and pressure). The liquid MAI·xMA 0 complex removed from MA 0 atmosphere desorbs MA 0 gas spontaneously until it transforms into a relative stable semi-solid-state with the x value of about 1.1, which is denoted as stage II. After further heating at 80°C for 10 min (Stage III), the sample returns to a white powder with the same weight as the initial MAI, which means the complete reversibility of absorptiondesorption process in MAI-MA 0 pair. In FAI-MA 0 pair, the Stage I and Stage II are similar to these of MAI-MA 0 pair, but the weight of the final powder in the Stage III cannot return back to the initial value of FAI because of the formation of MFAI and DMFAI as presented in Fig. 2a. FAI powder exposed to NH 3 gas atmosphere rapidly achieves a liquid phase FAI·xNH 3 (Supplementary Fig. 18) with the x value of ∼3.0 (Stage I). The liquid phase transforms into an ice-like transparent solidstate FAI·xNH 3 with x ∼ 1.3 as NH 3 desorption in Stage II and the XRD pattern of the ice-like complex is shown in Supplementary Fig. 17. The following thermal annealing at 80°C fully removes the absorbed NH 3 molecules and leads to the formation of a white powder with the same weight as the initial FAI (Stage III). This phenomenon, similar to that of MAI-MA 0 pair, preliminarily indicates the feasibility of the NH 3 as a post-healing gas for FA-based perovskite films.
To make a profound study, the chemical reaction and intermolecular interactions between FAPbI 3 precursors and NH 3 molecules, the solution 15 N NMR spectra are measured as shown in Fig. 2b Supplementary Fig. 3). The reaction process between the NH 3 and FAI is similar to the transimination reaction involving the aliphatic amine. The lone-pair electrons of N atom in NH 3 can attack electrophilic imine bond in FAI,   Supplementary Fig. 25. NH 3 , employed as a post-healing gas, should also have good solubility for the FA-based perovskite precursors, including PbI 2 and FAI powders. The color of mixed PbI 2 /FAI powder exposed in NH 3 gas atmosphere turns into light yellow from the yellow of PbI 2 at 20°C 36 . The mass difference before and after absorption shows that the absorbed NH 3 molecule number per FAPbI 3 is ∼4. While FAPbI 3 ·4NH 3 is still a solid-state rather than an expected liquid state, which is very different from liquid MAPbI 3 ·xMA with x of only 3 17 . One possible reason is the much smaller size of NH 3 than MA 0 . We have found that the absorbed amount of gas is highly dependent on processing temperature 23 . Lowering the processing temperature to −5°C leads to the formation of a white powder with x value of ∼6. At −15°C, a flowable slurry with the x value of ∼12 is formed, as shown in Fig. 2d.
The kinetic process of NH 3 desorption from the flowable FAP-bI 3 ·xNH 3 complex is measured by monitoring its weight change with temperature increased step-by-step from 20°C to 120°C under an open condition. The absorbing NH 3 number per FAPbI 3 as the function of time illustrated in Fig. 2e shows that the weight of FAPbI 3 ·xNH 3 slurry drops rapidly at the initial stage and then decreases slowly in 30 min at 20°C. Then the sample was annealed at 40°C for 30 min and 60°C for 30 min showing continuously slow weight loss by weighing at regular intervals. At 80°C, the sample quickly reaches a relatively stable state then almost no weight loss in the maintained 30 min and the NH 3 molecular number per FAPbI 3 is about 1.0. Finally, the x value quickly decreases to 0 when the sample is annealed at 120 C.

Preparation and characterization of thin films
Then the NH 3 post-healing strategy is employed to prepare FAbased perovskite films based on a homemade chamber with a semiconductor chilling plate controlling chamber temperature ( Supplementary Fig. 26). As shown in Supplementary Fig. 27a, b, the raw FAPbI 3 film with voids by the traditional one-step spin-coating method can transform into a uniform film after NH 3 post-healing at −15°C. The NH 3 post-healing FAPbI 3 is denoted as NH 3 -FAPbI 3 . The XRD spectra show that the NH 3 -FAPbI 3 film has better crystallinity and less undesired δ phase than the raw film ( Supplementary  Fig. 27c). This leads to the increasing PCE of the NH 3 -FAPbI 3 device compared to the raw-FAPbI 3 device (Supplementary Fig. 27d). While the PCE of NH 3 -FAPbI 3 device is still limited due to the existence of undesired δ-phase in the perovskite film. To prepare highly efficient PSCs, cesium (Cs) doped FAPbI 3 material system FA 0.9 Cs 0.1 PbI 3 (FACsPbI 3 ) is selected. The NH 3 post-healing process of FACsPbI 3 film is schematically illustrated in Fig. 3a. Due to the thin thickness of perovskite films, the NH 3 gas absorption and desorption are much easier and faster than those of powder samples. The SEM images show that the raw FACsPbI 3 film could be well healed by the NH 3 post-healing method in the temperature range from −15°C to 0°C, and −15°C was used for NH 3 gas post-healing in the following study ( Supplementary Fig. 28).  The scanning electron microscope (SEM) image (Fig. 3b) shows that there are some micrometer-scale voids in the raw FACsPbI 3 film. While the NH 3 -FACsPbI 3 film is dense and smooth (Fig. 3c), resulting from the self-leveling of the liquid intermediate state and the quick desorbing process of the NH 3 . This gas post-healing treatment with the self-leveling behavior is essentially different from the traditional posttreatment using DMF 37 , MASCN vapor 25 , etc. The corresponding atomic force microscope (AFM) images ( Supplementary Fig. 29) show that the root mean square (RMS) roughness of NH 3 -FACsPbI 3 film is only 9 nm over a 20 × 20 µm 2 area, which is even lower than that of the film prepared by the traditional antisolvent method (24 nm) (denoted as anti-FACsPbI 3 ).
X-ray diffraction (XRD) patterns in Fig. 3d and e show that the NH 3 post-healing strategy can improve the orientation of the perovskite film, and the diffraction intensity of (110) peak of the NH 3 -FACsPbI 3 perovskite film is about 100 times stronger than that of the raw FACsPbI 3 perovskite film. Besides, NH 3 post-healing decreases the full-width half-maximum (FWHM) of the (110) peak from 0.203 o to 0.114 o (Fig. 3e). As shown in ultraviolet-visible (UV-Vis) optical absorption spectra (Fig. 3f) and their Tauc plot curves ( Supplementary Fig. 30), the raw and NH 3 -FACsPbI 3 perovskite films present almost the same absorption edge and band gap of 1.54 eV. While the absorbance of NH 3 -FACsPbI 3 perovskite film exhibits an obvious increase compared to that of raw perovskite film, resulting from the removal of voids. Photoluminescence (PL) peak of the NH 3 -FACsPbI 3 film is similar to that of the anti-FACsPbI 3 film (Supplementary Fig. 31), but obviously blue shift and narrow in comparison with the raw FACsPbI 3 film, which indicates a low trap density of NH 3 -FACsPbI 3 and anti-FACsPbI 3 films in comparison with the raw film 38 . The reduced defect density is also evidenced by the charge-limited current (SCLC) and timeresolved photoluminescence (TRPL) results in Supplementary  Fig. 32. The calculated defect density from the SCLC curves decreases from 3.97 × 10 16 to 9.62 × 10 15 cm −3 . And the TRPL results show that the NH 3 -FACsPbI 3 film has a much longer trap-assisted nonradiative lifetime (τ = 5.6 μs) than the Raw FACsPbI 3 film (τ = 3.2 μs).
To further evaluate the device stability based on NH 3 posthealing treatment, the high-efficiency NH 3 -FACsPbI 3 , anti-FACsPbI 3 , anti-FA 0.90 Cs 0.05 MA 0.05 PbI 3 (anti-FMCsPbI 3 ), and anti-MAPbI 3 PSCs are employed. As the low PCE, raw FACsPbI 3 device has not been chosen to study its stability. The shelf stability of unencapsulated devices in Fig. 4e shows that NH 3 -FACsPbI 3 device has negligible performance loss after 320 days of storage, which is similar to the   Article https://doi.org/10.1038/s41467-022-32047-z anti-FACsPbI 3 devices and much better than anti-FMCsPbI 3 and anti-MAPbI 3 . The XRD and UV-Vis spectra of these aged perovskite films in 320-day-aged PSCs  show that NH 3 -FACsPbI 3 film keeps its strong light absorption, and has few PbI 2 . Meanwhile, NH 3 -FACsPbI 3 device still maintains decent crosssectional morphology with clear grain boundaries ( Supplementary  Fig. 42). What's more, the maximum power point (MPP) of the unencapsulated NH 3 -FACsPbI 3 , anti-FACsPbI 3 , anti-FMCsPbI 3, and anti-MAPbI 3 PSCs is tracked under white light emitting diode (LED) irradiation (Fig. 4f, Supplementary Fig. 43) with an intensity equivalent to 1 sun in N 2 atmosphere. After 500 h of continuous light soaking, the NH 3 -FACsPbI 3 device maintains 80% of its initial efficiency, and the stability trend of MPP tracking is consistent with that of shelf stability in these devices.

Discussion
We have systematically studied the transimination reactions between FA/RA gases and FAI salt, and further developed an NH 3 gas posthealing strategy for upscale fabrication of high-quality FA-based perovskite films. The low operating temperature during NH 3 posthealing process is vital to enable FA-based perovskite materials to absorb enough NH 3  module is up to 20.61%. Meanwhile, the device stability based on this strategy is also comparable with that of the state-of-the-art antisolvent method. This NH 3 gas post-healing technology is compatible with established commercial technologies to efficiently remove voids in the raw FA-based films and therefore opens a direction for fabrication of large-scale high-efficient FA-based PSCs.

Material synthesis
For the synthesis of N-methyl formamidinium iodide (MFAI), Methylamine alcohol solution (30-33 wt. % in anhydrous ethanol, 425 μl, about 2.8 mmol) was added dropwise to a solution of formamidinium iodide (FAI, 516 mg, 3 mmol) in 30 ml anhydrous ethanol under nitrogen protection, and the mixture was stirred at 0°C for 2 h. Subsequently, the solvent was evaporated under reduced pressure and the residue was recrystallized in the mix solvent of isopropanol and ethyl acetate in glove box to obtain the MFAI powder. The synthesis of N, N'-dimethyl formamidinium iodide (DMFAI) was similar to that of MFAI, but the amount of the methylamine alcohol solution was increased to 1 ml.

NMR sample fabrication
For solution 1 H NMR characterization of the sample in Table 1 (No.1), the mixture of 5.0 g FACl and 5.0 g NaOH was reacted at RT in a conical flask, and the generated gas was collected by 0.5 ml DMSO-d 6 . For samples in Table 1 (No. 2-4), the mixture of 5.0 g FACl and 5.0 g NaOH was reacted at 150°C, and the generated gas was collected by 0.5 ml DMSO-d 6 , 1 ml HOAc or 0.2 g FAI powder at RT. Samples No. 3 and 4 were vacuumed before dissolving in DMSO-d 6 . For samples in Table 1 (No. 5-12), the gas sources of R-NH 2 were heated at 60°C, and the generated gases were collected by 0.2 g FAI powder. The gas sources of R-NH 2 were methylamine alcohol solution, the mixture of EACl and NaOH, PA, BA, NH 3 15 N NMR characterization, 15 NH 3 was produced from the reaction between 5.0 g 15 NH 4 Cl (10% 15 N labelled) and 5.0 g NaOH at 60°C, and the generated gas was collected by 0.5 ml DMSO-d 6 . FAI ( 15 N) was produced based on the reaction between 0.2 g FAI and excess 15 NH 3 at RT for 6 h, followed by vacuum treatment. FAI·x 15 NH 3 , PbI 2 ·x 15 NH 3 , and FAPbI 3 ·x 15 NH 3 were generated between the reaction between 0.2 g FAI, 0.2 g PbI 2 , or 0.2 g FAPbI 3 precursor powders and excess 15 NH 3 at RT for 6 h, but without vacuum treatment.
The above samples were directly dissolved in DMSO-d 6 for 15 N NMR measurement.
The NMR sample fabrication of FAPbI 3 ·x 15 NH 3 for the solid-state NMR spectrum was similar to that of the solution 15 N NMR spectrum, but 15 N isotope source for preparing 15 43 . The HPEDC pulse sequence was used. The acquisition time was 50 ms, the spin rate was 3 kHz, and the recycle delay was 5 s. The two-pulse phase-modulation (TPPM) decoupling was used during the acquisition.

Perovskite film fabrication
Raw FACsPbI 3 films: The perovskite precursor was prepared by mixing PbI 2 : FAI: CsI (1:0.9:0.1 molar ratio) in DMF solvent (1.40 M). Raw FAPbI 3 films: The perovskite precursor was prepared by mixing PbI 2 : FAI (1:1 molar ratio) in DMF solvent (1.40 M). The raw FACsPbI 3 and FAPbI 3 films were simply fabricated by one-step spin-coating at 4000 rpm for 30 s and then heated at 140°C for 20 min. NH 3 -FACsPbI 3 film: After spin-coating, the raw FACsPbI 3 film was annealed at 140°C for 5 min, and then transferred into a homemade chamber with a temperature from 20 to −15°C. N 2 gas was used to remove the moisture-laden air in the chamber. Subsequently, NH 3 gas was quickly introduced into the chamber and maintained for ∼5 s. Then the NH 3 gas is removed from the chamber and the film was further annealed at 140°C for 20 min. For NH 3 -FAPbI 3 film, the film treatment process is the same as above, and the temperature of the homemade chamber is −15°C for NH 3 post-healing process.
For anti-FACsPbI 3 , anti-FMCsPbI 3 , and anti-MAPbI 3 films, the perovskite precursors were prepared in DMF: DMSO (3:7, 1.40 M) by stoichiometric ratios. The perovskite solution was spin-coated in a two-step at 1000 rpm and 4000 rpm for 10 s and 30 s, respectively. During the second step, 300 μl anisole was drop-casted quickly at the tenth second of the second step. The anti-MAPbI 3 perovskite film was then heated at 100°C for 20 min, and the other films were heated at 140°C for 20 min.
The α-FAPbI 3 , δ-FAPbI 3 , MFAPbI 3 , and DMFAPbI 3 films were fabricated from their DMF solution with a concentration of 1.40 M using chlorobenzene as the antisolvent. The α-FAPbI 3 , MFAPbI 3 , and DMFAPbI 3 films were obtained after heating treatment at 140°C for 20 min. The δ-FAPbI 3 film was achieved by exposing α-FAPbI 3 film in the air (RH > 50%) until fully transformed into yellow. The MA-FAPbI 3 film was prepared by the MA 0 gas post-healing the α-FAPbI 3 film and then heated at 140°C for 20 min.
The annealing process of all thin films is in ambient air conditions (30-40% humidity).

Device fabrication
The methods described are similar to that reference 44. Fluorine doped tin oxide (FTO)-coated glass (2.20 mm, 7Ω sq −1 ) was used as the substrate for the devices. The compact TiO 2 layer (∼10 nm) was deposited by atomic layer deposition (ALD) for 200 cycles and annealed at 500°C for 30 min in ambient air. For ALD TiO 2 deposition, titanium (IV) isopropoxide (TTIP) and H 2 O as Ti and O sources, respectively. The TTIP precursor was held at 75°C. Pulse/exposure/ purge times of 1 s/8 s/25 s were used for the TTIP and 0.1 s/8 s/25 s for H 2 O precursor, and the deposition temperature was set to 120°C. On top of the c-TiO 2 layer, SnO x -Cl layer was deposited by spincoating at a speed of 3000 rpm for 30 s from an aged SnCl 4 aqueous solution (1:75 with deionized water by volume), followed by a sintering heat-treatment of 200°C for 30 min in air and then transferred to the glove box for device fabrication. The perovskite layers were fabricated as described above. For the surface passivation, 1 mg ml −1 of Phenyltrimethylammonium tribromide (PTAB) solution in isopropanol was spin-coated on these perovskite films at 4000 rpm for 30 s.
For fabricating modules, P1 etching process was pre-patterned on FTO glass (5 cm × 5 cm) with a 1064 nm fiber laser (Han's laser). The laser power ratio, laser duty cycle, and laser frequency were 30%, 5%, and 50 kHz, respectively. Then, patterned FTO substrates were cleaned and treated by UV Ozone Cleaner (Ossila) for 15 min. The TiO 2 /SnO 2 , PTAB, and Spiro-OMeTAD layers were prepared with the same procedure as presented above. The large-size raw FACsPbI 3 perovskite film was prepared through the doctor-blading method (provided by Suzhou GCL Nano Co. Ltd.). The NH 3 post-healing strategy was carried out on it to form a large-scale NH 3 -FACsPbI 3 film. For P2 etching process, the laser used was a 532 nm laser with a laser power ratio of 65%, a laser duty cycle of 5%, and a laser frequency of 100 kHz. 80 nm thick Au electrodes were thermally evaporated under vacuum to complete the modules fabrication. Finally, P3 etching used the same laser with P2 with a laser power ratio of 50%, a laser duty cycle of 5%, and a laser frequency of 100 kHz. P4 is an etching procedure for cleaning the edge of the modules, the laser used in P4 is the same with P1 with a laser power ratio of 40%, the laser duty cycle of 10%, and a laser frequency of 100 kHz.
Perovskite film and device characterization The characterization described are similar to that reference 44. XRD spectra were measured by Ultima IV of Rigaku with Cu Kα radiation (1.5406 Å). The UV-Vis absorbance spectra were measured by QE Pro (Ocean Optics). Top view, cross-section SEM images were obtained with a field-emission SEM (S-4800, Hitachi). Steady PL spectra were recorded on QE Pro excited at 460 nm. AFM measurements were performed in contact mode (5400, Agilent). EQE measurement was calculated using certified incident photon to current conversion efficiency equipment from Enlitech (QE-R). Time-resolved photoluminescence (TRPL) experiments were performed by Steady State and Transient State Fluorescence Spectrometer (Edinburgh FLS980). The testing conditions as the films were photoexcited at 483.6 nm pulse width ∼ 118.6 ps, 5 mW/pulse, and emission were collected on the surface side of the film (perovskite/ glass substrate).
J-V curves of the as-fabricated PSCs were measured using a SourceMeter (Keithley 2400) under simulated one-sun AM 1.5 G 100 mW cm −2 intensity (Oriel Sol3A Class AAA, Newport) with a scan rate of 200 mV/s (the voltage step is 20 mV with no delay time) from reverse and forward two scanning directions in air condition around 25°C. The typical active area of PSCs is 0.09 cm 2 defined by a metal mask. The area of the mask (0.08713 cm 2 ) used for certification was certified by the National Institute of Metrology, China, No. CDjc2021-10891. The intensity of one-sun AM 1.5 G illumination was calibrated using a Si-reference cell certified by the National Renewable Energy Laboratory. SPO is measured by tracking the current under a fixed voltage which is decided by the voltage of maximum power point at the J-V curve. Here, the fixed voltage of NH 3 -FACsPbI 3 device is 1.002 V.
For the stability tests, all PSCs were without encapsulation. For shelf-life stability, the devices were stored in a dark environment with a humidity of 10-30%, and the photovoltaic performance of PSCs was measured every ten days. The operational stability was performed using a stability setup (LC Auto-Test 24, Shenzhen Lancheng Technology Co., Ltd.), tested under continuous light illumination and maximum power point tracking (controlled and monitored to be 15°C). The light source consisted of an array of white LEDs powered by a constant current. The LED type is MG-A200A-AE with an emission spectrum of 400-750 nm (Supplementary Fig. 40). Equivalent sun intensities were calibrated using a calibrated Si-reference cell. During aging, the device is connected with a 100 Ohm load resistance. The PSCs were masked and placed inside a sample holder purged with continuous N 2 flow. J-V curves with reverse voltage scans were recorded every 12 h during the whole operational test.

Reporting summary
Further information on research design is available in the Nature Research Reporting Summary linked to this article.

Data availability
Data that support the findings of this study are available in Supplementary Data Files in the Supplementary Information section. Source data are provided with this paper.